PC hangs often

I am new to techspot. My pc hangs often and really having problem. I would like to know if this is my pc problem, or malware or spyware issue or something else...

My PC processor is AMD Athlon XP 1800+ 1.53 GHz, 2 GB RAM. I purchased this from my colleague and is not here. It seems he re-installed english version of Windows XP later which didn't come with it, when he purchased my desktop.

I did defragementation and is using Avira free editoin of anti-virus. I also uninstalled some unused programs and there is 13GB space left in C and some 1.9GB in D. My virtual memory directory is C and its size is 2GB to 4GB.